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Dendrimer Generation (dendrimer + generation)
Selected AbstractsControl of Charge Transport in Iridium(III) Complex-Cored Carbazole Dendrimers by Generation and Structural ModificationADVANCED FUNCTIONAL MATERIALS, Issue 2 2009Salvatore Gambino Abstract Here, the charge transporting properties of a family of highly phosphorescent iridium(III) complex-cored carbazole dendrimers designed to have improved charge transport by incorporating carbazole units into the dendrons are studied. Firstly, the effect of the dendrimer generation and the role of dendron for materials with one dendron per ligand of the core are considered. It is shown, in contrast to previously reported light-emitting dendrimers, that in this case the carbazolyl-based dendrons have an active role in charge transport. Next, the effect on the charge transport of attaching two dendrons per ligand to the dendrimer core is explored. In this latter case, for the so called "double dendron" material a highly non-dispersive charge transport behavior is observed, together with a time-of-flight mobility of the order of 10,3,cm2 V,1,s,1. Furthermore the lowest energetic disorder parameter (,) ever reported for a solution-processed conjugated organic material is found, ,,< ,20 meV. [source] Robust and Responsive Dendrimer,Gold Nanoparticle Nanocomposites via Dithiocarbamate CrosslinkingADVANCED MATERIALS, Issue 22 2009Myoung-Hwan Park A simple and reliable one-step technique is developed to form robust PAMAM dendrimer,gold nanoparticle nanocomposites using dithiocarbamate-based chemistry. The interparticle spacing and optical properties of films can be readily tuned by controlling the dendrimer generation and/or the mole ratio between dendrimers and nanoparticles. The technique is also used to obtain patterned materials on prepatterned surfaces. [source] Solution and Thin-Film Aggregation Studies of Octasubstituted Dendritic PhthalocyaninesISRAEL JOURNAL OF CHEMISTRY, Issue 1 2009Casey A. Kernag The synthesis and solution and thin-film characterization of eight octasubstituted dendritic phthalocyanines (Pcs) and their zinc complexes are reported. The Pc chromophore was substituted in the 2,3,9,10,16,17,23,24-positions with three generations of benzylaryl ether dendrons with either a benzyl (3a-3c) or 3,5-di- t -butylbenzyl periphery (3d-3f). Visible spectra in solution (CH2Cl2 -EtOH mixtures, toluene, THF, dioxane, acetone, and EtOAc) indicated a varying degree of chromophore aggregation that depended on solvent, dendrimer generation, and whether the Pc was metallated. Variable-concentration visible spectroscopic studies were analyzed using a nonlinear least-squares fitting procedure giving Kd values. These values further quantitated the observations that the t -butyl-substituted den-drimers 3d-3f were all less prone to aggregation in solution than the unsubstituted dendrimers 3a-3c, with a monotonic decrease in Kd across the series 3a , 3b , 3c , 3d , 3e , 3f. Second-generation t -butyl-substituted dendrimer 3f showed little to no aggregation in all solvents studied. Thin-film studies indicated that the largest members of the two dendrimer groups, third-generation 3c and second-generation 3f, were largely monomeric as evidenced by split Q-bands, similar to that seen in dilute CH2Cl2 solution when deposited via spin-coating onto glass slides. The metallated zinc Pcs 4a-4f all exhibited significantly less tendency toward aggregation in both solution and thin-films than their unmetallated analogues. [source] Novel materials for bioanalytical and biomedical applications: Environmental response and binding/release capabilities of amphiphilic hydrogels with shape-persistent dendritic junctions,JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2005Chao Zhu Abstract The binding and release capabilities of a hydrogel series, constructed of hydrophilic poly(ethylene glycol) segments and hydrophobic dendritic junctions [poly (benzyl ether)s], are evaluated in aqueous media. The environmental response of the amphiphilic networks is also tested in water at three pH values: 1.5, 7.0, and 10.1. The highest swelling ratio is observed under acidic conditions and varies between 3.7 and 6.5, depending on the crosslinking density and dendrimer generation. Gel specimens with embedded indicators react within 3,6 s with a clear color switch to the change in the pH of the surrounding medium. The experiments with model anionic and cationic indicators and stains show that the hydrogels have basic interiors. The gel binding capabilities depend on the water solubility of the substrate and on the size of the incorporated dendritic fragments. Model release studies have been performed at 37 °C and pHs 1.5, 7.0, and 10.1. The observed phenomena are explained by the transformations in the structure and charge that both the networks and the model compounds undergo with the changes in the pH of the aqueous medium. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4017,4029, 2005 [source] Synthesis of carbohydrate-linked poly(polyoxometalate) poly(amido)amine dendrimersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2005Joel R. Morgan Abstract Mannose-functionalized and ethoxyethanol-functionalized poly(amido)amine dendrimers bound multiple vanadate-substituted polyoxotungstate Wells,Dawson-type polyoxometalates (POMs). Dendrimers incorporating 10,30 POMs were characterized with NMR, transmission electron microscopy, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry techniques. The number of metal clusters per dendrimer molecule varied according to the dendrimer generation and the nature of the surface functional groups. Efforts aimed at using the poly(polyoxometalate) dendrimers as oxidation catalysts are also described. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3059,3066, 2005 [source] Synthesis of an oligosaccharide,polylysine dendrimer with reducing sugar terminals leading to acquired immunodeficiency syndrome vaccine preparationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2005Huricha Baigude Abstract A novel cellobiose,polylysine dendrimer with reducing sugar terminals was synthesized in which the reactive reducing end of a disaccharide cellobiose was directing outward. Hexa- O -benzyl-4,-(1-carboxyethyl)-cellobioside (HBCEC) was synthesized through the reaction of a 4,-hydroxyl group of benzyl hexa- O -benzyl-cellobioside with methyl 2-chloropropionate, followed by the removal of the methyl ester group. HBCEC was reacted with polylysine dendrimer generation 3 (G3) to produce benzylated cellobiose,polylysine dendrimer G3. After debenzylation, a cellobiose,polylysine dendrimer G3 was obtained in which the reducing end of the cellobiose was the terminal group of the dendrimer. For the preparation of a dendrimer-type acquired immunodeficiency syndrome vaccine, the cellobiose,polylysine dendrimer was reacted with a tripeptide (glycyl,prolyl,leucine) and a cyclic oligopeptide from the human immunodeficiency virus by reductive amination; this produced a tripeptide-bound cellobiose,polylysine dendrimer and an insoluble compound, respectively. The structure analysis was carried out with NMR and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2195,2206, 2005 [source] PAMAM dendrimer-based contrast agents for MR imaging of Her-2/neu receptors by a three-step pretargeting approachMAGNETIC RESONANCE IN MEDICINE, Issue 4 2008Wenlian Zhu Abstract Pretargeting of receptors is a useful approach in molecular imaging and therapy to reduce background noise or toxicity and enhance selectivity. In this study a three-step pretargeting approach that includes a biotinylated antibody, avidin/streptavidin, and a biotinylated imaging agent is described. A PAMAM dendrimer generation 4 (G4D)-based MRI T1 agent biotin-G4D-DTPA-Gd (bG4D-Gd) and its sister compound with remaining free surface amine groups blocked by succinic anhydride to reduce positive charges (bG4D-Gd-SA) were synthesized. Limited selective enhancement in MRI was observed in a Her-2/neu mouse tumor xenograft by this three-step pretargeting approach that includes biotinylated trastuzumab, avidin and bG4D-Gd, or bG4D-Gd-SA. However, these dendrimer-based MRI agents with molecular weight around 29 kD reached and remained in the tumor through the enhanced permeability and retention effect. Prolonged and extensive accumulation of both bG4D-Gd and b-G4-Gd-SA in the kidneys was also observed. Magn Reson Med, 2008. © 2008 Wiley-Liss, Inc. [source] Molecular weight determination of ultra-high mass compounds on a standard matrix-assisted laser desorption/ionization time-of-flight mass spectrometer: PAMAM dendrimer generation 10 and immunoglobulin MRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2006Roland Müller First page of article [source] Diffusion and NOE NMR Studies on Multicationic DAB-Organoruthenium Dendrimers: Size-Dependent Noncovalent Self-Assembly to Megamers and Ion Pairing,CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2009Stefania Pettirossi Dr. Abstract Supra-mega ion pairing: Multicationic organoruthenium dendrimers show a notable tendency to self-aggregate when the concentration is increased, leading to megamers. This tendency increases with the generation. The self-aggregation of dendrimers to megamers is coupled with a decrease in the extent of ion pairing, as illustrated. New multicationic organoruthenium dendrimers (RuPF6 -Dabn, n=2, 4, 8, 16) have been synthesized by coupling of [Ru(,6 - p -cymene)(,3 -dpk-OCH2CH2OH)]X (1PF6, dpk=2,2,-dipyridyl ketone, X=PF6) with 1,4-diaminobutane (DAB) and polypropylenimine dendrimer DAB- dendr -(NH2)n {n=4, 8, 16} mediated by 1,1,-carbonyldiimidazole (CDI). The intermediate in the synthesis, [Ru(,6 - p -cymene)(,3 -dpk-OCH2CH2OC(O)Im]X (2PF6, Im=imidazole, X=PF6) has been isolated and characterized by single-crystal XRD. The intra- and supramolecular structures in a solution of RuPF6 -Dabn dendrimer have been investigated by multidimensional and multinuclear NMR techniques. Diffusion NMR experiments on dilute solutions indicated that the linear distance between two metal centers (14.9,22.1,Å depending on the dendrimer generation) is much greater than the diameter of 1PF6 (9.9,Å). 19F,1H-HOESY NMR experiments (HOESY= heteronuclear Overhauser effect spectroscopy) showed that the counterion is positioned on the surface of the dendrimers and assumes the same relative anion,cation orientation as in 2PF6. Diffusion NMR experiments on RuPF6 -Dabn dendrimers in CD2Cl2 at different concentrations revealed a process of supramolecular assembly of dendrimers to megamers that is strongly favored for the highest generations. Megamer formation is coupled with an increased fraction of free ions (,) and a consequent reduction in ion-paired ruthenium centers. Graphs of , versus CRu (the concentration of ruthenium centers) showed a minimum for RuPF6 -Dab4, RuPF6 -Dab8, and RuPF6 -Dab16 at a position coinciding with the significant presence of supramolecular dendritic dimers. The tendency to ion pairing decreases as the dendrimer generation increases. [source] Increased Efficacies of an Individual Catalytic Site in Clustered Multivalent Dendritic CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Govindasamy Jayamurugan Abstract In the studies reported so far on dendrimer-mediated catalysis, the efficacies of the catalytic units were studied and compared primarily across the generations. In order to identify the efficacy of an individual catalytic unit with respect to the number of such units present within a given generation, a series of catalysts were prepared within a generation. Dendrimers incorporated with phosphine-metal complexes were chosen for the study and as many as 11 catalysts within three generations were synthesized. The CC bond-forming reactions, namely, the Heck and the Suzuki coupling reactions, were then selected to study the catalytic efficiencies of the series of partially and fully phosphine-metal complex functionalized dendrimers. The efficacies of the formation of cinnamate and biphenyl, catalyzed by the dendritic catalysts, were compared. The comparative analyses show that an individual catalytic site is far more effective in its catalytic activity when presented in multiple numbers, i.e., in a multivalent dendritic system, than as a single unit within the same generation, i.e., in a monovalent dendritic system. The study identifies the beneficial effects of the multivalent presentation of the catalytic moieties, both within and across the dendrimer generations. [source] Preparation and study of cellulose acetate membranes modified with linear polymers covalently bonded to Starburst polyamidoamine dendrimersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008J. Ledesma-García Abstract Novel ion-selective membranes were prepared by means of the noncovalent modification of a cellulose acetate (CA) polymer with either poly(ethylene- alt -maleic anhydride) or poly(allylamine hydrochloride) chains covalently linked to Starburst amine-terminated polyamidoamine (PAMAM) dendrimers generations 4 and 3.5, respectively. Linear polymer incorporation within the porous CA membrane was performed with mechanical forces, which resulted in modified substrates susceptible to covalent adsorption of the relevant dendritic materials via the formation of amide bonds with a carbodiimide activation agent. The membranes thus prepared were characterized by chemical, physical, and spectroscopic measurements, and the results indicate that the dendrimer peripheral functional groups were the species that participated in the ion-exchange events. The prepared materials were also evaluated for their ion-exchange permeability with sampled current voltammetry experiments involving cationic and anionic species {[Ru(NH3)6]3+ and [Fe(CN6)]3,, respectively} as redox probe molecules under different pH conditions. As expected, although permeability was favored by opposite charges between the dendrimer and the electroactive probe, a clear blocking effect took place when the charge in the dendritic polymer and the electroactive complex was the same. Electrochemical impedance spectroscopy measurements, on the other hand, showed that the PAMAM-modified membranes were characterized by good selectivity and low resistance values for multivalent ions compared to a couple of commercial ion-exchange membranes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] A structure/function study of polyaminoamide dendrimers as silica scale growth inhibitorsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2005Konstantinos D Demadis Abstract Dendrimers have attracted immense attention during the last decade due to their interesting properties both from a basic and an applied research viewpoint. Encapsulation of metal nanoparticles for catalysis, drug delivery and light harvesting are only some applications of dendrimers that are breaking new ground. A novel application of dendrimer technology is described in the present paper that relates to industrial water treatment. Industrial water systems often suffer from undesirable inorganic deposits. These can form either in the bulk or on metallic surfaces, such as heat exchangers or pipelines. Silica (SiO2) scale formation and deposition is a major problem in high-silica-containing cooling waters. Scale prevention rather than removal is highly desired. In this paper, benchtop screening tests on various silica inhibition chemistries are reported, with emphasis on materials with a dendrimeric structure. Specifically, the inhibition properties of commercially available STARBURST® polyaminoamide (PAMAM) dendrimers generations 0.5, 1, 1.5, 2, and 2.5 are investigated in detail together with other commonly-used scale inhibitors. Experimental results show that inhibition efficiency largely depends on structural features of PAMAM dendrimers such as generation number and nature of the end groups. PAMAM dendrimers are effective inhibitors of silica scale growth at 40 ppm dosage levels. PAMAM dendrimers also act as silica nucleators, forming SiO2,PAMAM composites. This occurs because the SiO2 formed by incomplete inhibition interacts with cationic PAMAM-1 and -2. The general scope of silica formation and inhibition in industrial waters is also discussed. Copyright © 2005 Society of Chemical Industry [source] | |||||||||||||||||||||||||